The quark is the elementary particles that combines with another quark and interacts through the strong interaction as color force to form hadrons like proton and neutron. There are six species of quarks, generally referred to as flavors. They are up and down quarks, charm and strange quarks, top and bottom quarks. The quarks have color charges that causes the color force. The color charges are arbitrarily given names as red, blue and green. For example, inside a proton, the two up quarks and the down quark change colors by emitting a gluon, which mediates the strong color force between them.
Frequently Asked Questions
Why is it impossible to observe quarks?
Quarks don’t exist individually due to color confinement. When a quark pair is separated, the gluon tubes between them increases and the energy become higher. At one point, this energy becomes greater than the energy required in creating a new antiquark matter. So the instant the gluon tubes separate, the isolated quark forms itself an antiquark to pair with, forming a meson. This the reason why quarks cannot be observed individually. But in particle accelerators, quarks can be observed as quark jets. However, it is believed that after the Big Bang the universe was in a state of quark–gluon plasma. On July 2015, the LHC produced quark-gluon plasma. In this state, the quarks are said to be deconfined.
How do we know that quarks exist for real?
In 1990, when electrons and hadrons were subjected to a form of inelastic collision called as the deep inelastic scattering at SLAC, the observations showed that the kinetic energy was not conserved after the collision. The high energy electrons on collision 'split' the hadron into its component particles, which are quarks. And due to color confinement, the free quarks immediately hadronized to form new hadrons. It is this observation of the hadron jet that made it clear that quarks do exist, providing the physical proof of quark model, which was only a mathematical model before this collision.